Mannose 6-Phosphate/Insulin-like Growth Factor–II Receptor Targets the Urokinase Receptor to Lysosomes via a Novel Binding Interaction

Abstract

The urokinase-type plasminogen activator receptor (uPAR) plays an important role on the cell surface in mediating extracellular degradative processes and formation of active TGF-β, and in nonproteolytic events such as cell adhesion, migration, and transmembrane signaling. We have searched for mechanisms that determine the cellular location of uPAR and may participate in its disposal. When using purified receptor preparations, we find that uPAR binds to the cation-independent, mannose 6-phosphate/insulin-like growth factor–II (IGF-II) receptor (CIMPR) with an affinity in the low micromolar range, but not to the 46-kD, cation-dependent, mannose 6-phosphate receptor (CDMPR). The binding is not perturbed by uPA and appears to involve domains DII + DIII of the uPAR protein moiety, but not the glycosylphosphatidylinositol anchor. The binding occurs at site(s) on the CIMPR different from those engaged in binding of mannose 6-phosphate epitopes or IGF-II. To evaluate the significance of the binding, immunofluorescence and immunoelectron microscopy studies were performed in transfected cells, and the results show that wild-type CIMPR, but not CIMPR lacking an intact sorting signal, modulates the subcellular distribution of uPAR and is capable of directing it to lysosomes. We conclude that a site within CIMPR, distinct from its previously known ligand binding sites, binds uPAR and modulates its subcellular distribution.

Demonstration of tumor suppression by mannose 6-phosphate/insulin-like growth factor 2 receptor

“…Man-6-P/IGF-2 receptor on the surface of tumor cells was shown to function as a death receptor for cytotoxic T-cell-induced apoptosis by mediating endocytosis of mannose phosphorylated granzyme B released by cytotoxic T cells (Motyka et al, 2000). Evidence for additional binding sites on the receptor for urokinase-type plasminogen activator receptor (uPAR) (Nykjaer et al, 1998), plasmin (Godar et al, 1999) and retinoic acid (Kang et al, 1997) has also been reported. Interaction of the receptor with uPAR appears to play a role in uPAR turnover (Nykjaer et al, 1998).…”

“…While initially characterized with respect to its role in lysosomal enzyme trafficking (Sahagian et al, 1981) and IGF-2 endocytosis (Tong et al, 1988), the receptor has been reported to be involved in a number of other growth-related processes including TGF-b activation (Dennis and Rifkin, 1991), growth suppression by retinoic acid (Kang et al, 1999), granzyme B-mediated cytotoxicity (Motyka et al, 2000), and uPA receptor turnover (Nykjaer et al, 1998). With the exception of granzyme B-mediated cytotoxicity, which is ruled out by the SCID mouse experiment described here, any or all of these functions could potentially be involved in tumor suppression.…”

“…Evidence for additional binding sites on the receptor for urokinase-type plasminogen activator receptor (uPAR) (Nykjaer et al, 1998), plasmin (Godar et al, 1999) and retinoic acid (Kang et al, 1997) has also been reported. Interaction of the receptor with uPAR appears to play a role in uPAR turnover (Nykjaer et al, 1998). The functional basis for interaction of retinoic acid with the receptor is unclear although evidence has been reported suggesting a role for the receptor in retinoic acid-dependent growth inhibition (Kang et al, 1999).…”

The mannose 6‐phosphate/insulin‐like growth factor II receptor restricts the tumourigenicity and invasiveness of squamous cell carcinoma cells

“…[8][9][10] Lysosomal sorting via M6P/IGF2R is generally far more efficient than by MPR46, demonstrating that the former is the main lysosomal targeting receptor in mammalian cells. 11,12 However, M6P/IGF2R also binds a variety of other factors that impinge on the proliferation, migration and invasiveness of tumour cells, including insulin-like growth factor II (IGF-II), 13 transforming growth factor b, 14 urokinase-type plasminogen activator receptor 15 and plasminogen. 16 Hence, it is of high relevance that the M6P/IGF2R gene is frequently inactivated in human and animal tumours.…”

Binding of Urokinase-type Plasminogen Activator Receptor (uPAR) to the Mannose 6-Phosphate/Insulin-like Growth Factor II Receptor

“…Several years ago, the Man-6-P/IGF2R was reported to bind uPAR via a novel interaction that was not inhibited by either Man-6-P or IGF-II (27,28). Binding of uPAR to the Man-6-P/ IGF2R was found to be a low affinity interaction (K D ϳ11 M) with a binding stoichiometry of ϳ1 mol of uPAR/mol of Man-6-P/IGF2R (27).…”